JavaScript is one of the most popular programming languages in existence but there are few tools for building applications with JavaScript or any other dynamic language. The tools that exist typically require a Web developer to download and install a product in order to get developer productivity features such as command completion suggestions (called INTELLISENSE® in the VISUAL STUDIO® development programs offered by MICROSOFT®), or the developer must simply make do without such features. This experience (requiring developers to download and install software) is contrary to the kinds of applications that JavaScript encourages, which are typically browser-based and can be accessed simply by visiting a Web page.
When developers want to know how something works, they typically read the documentation. The process of creating documentation is often laborious, however, involving not just the developer of the feature in question but writers and editors who actually create the documentation. Most developers have already included substantial information in their source code in the form of comments.